<!DOCTYPE html> 
<html lang="en">
<head>    
	<meta charset="UTF-8" /> 
    <title>背景半透明设置</title>
	<base target="_blank"/>
	<style>
		.alpha {
			width: 300px;
			height: 100px;
			background: rgba(218, 68, 68, 0.2);
			color:white;
			text-align: center;
			line-height: 100px;
		}
		.box {
			width: 300px;
			height: 100px;
			background: rgb(0, 0, 0);
			color:white;
			text-align: center;
			line-height: 100px;
		}
		body {
			background-color: green;
		}
	</style>
</head>
<body>
<body>
	<div class="alpha">
		背景半透明设置
	</div>
	
	<div class="box">
		背景半透明设置对照组
	</div>
</body>
</html>